Masonry units, such a blocks, are fabricated in a sequential process, using improved mold structures, such as within a production corridor of a corresponding fabrication system. A compressible masonry feedstock or formula, which can be de-agglomerated before use, is filled within a block mold having releasable elements. The formula is then compressed within the mold structure. The compressed workpiece can be further processed, such as for any of final height adjustment, the establishment of a surface feature, or to remove cores. The block mold, having releasable elements or sides, such as using hinges or springs, is released from the formed block, wherein the formed masonry unit can be removed for curing, and wherein the block mold can be reused to fabricate a subsequent masonry unit.